1. Field of the Invention
The present invention relates to spark gap devices, and particularly to such devices designed for surge diverters with magnetic blow-out, wherein a number of axially stacked discs of arc-resistance insulating material are spaced and support metallic electrodes connected through holes in each of the discs to form spark gaps.
2. Prior Art
In a spark gap for surge diverters of the kind referred to above, the arc is extended between insulating discs of arc-resistant, usually ceramic, material. The electrodes for the base points of the arc are attached to the discs, which are fixed in relation to each other by fitting protrusions on a disc into corresponding recesses on an adjacent disc. The spark-over distance between the electrodes thus becomes dependent on the ceramic tolerances and variations therein, which can be relatively great, among other things because the press tool for the manufacture of the discs is subjected to wear. As it is very important that the variations of the spark-over voltage is small, the aforementioned tolerances and variations therein are disadvantageous factors.
In the frequently used type of spark gap arrangements having stackable discs, in which the electrodes forming a spark gap are only attached on one disc each, four tolerances and variations therein are possible, namely, two in the vicinity of the rivet holes of the two discs, and two in the vicinity of the protrusions and recesses on the discs.
Attempts has been made to improve the above-mentioned disadvantage, among other things by different ways of attaching electrodes belonging to the same gap to one disc, for example by gluing and riveting. In this way the advantage is gained that the spark-over voltage is not controlled by the play between the discs. However, these solutions usually result in more complicated and expensive manufacture, and furthermore the ability of the discs to become stacked is restricted.
In the type of spark gas discs which are normally used at present, the fastening of the electrodes to the more or less brittle ceramic material also involves difficulties. Up to now, the electrodes have normally been fixed by riveting using specially made copper rivets. Such riveting is difficult to perform since, on the one hand, the pressure that can be used is limited with respect to the strength of the discs, whereas on the other hand a good electrical contact must be created between the rivet and the electrodes, since the passage of current between the electrodes takes place via the rivet.